In the photolithography technology, a process of making a semiconductor device or a liquid crystal display includes a step at which a pattern is formed by irradiating light onto a semiconductor wafer or an original plate (for liquid crystal) coated with resist; if, however, a foreign matter is adhered to the lithography mask or the reticle used on this occasion (hereinafter collectively referred to as “photomask”), this foreign matter absorbs light or bends light, whereby the transferred pattern becomes deformed or the edges become coarse, and the base becomes dirty black with the resulting problems of impaired size, quality, appearance and the like.
Though this process is usually performed in a clean room, it is still difficult to keep the exposure original plate clean at all times; therefore, in general, a means called pellicle for fending off foreign matters is installed on the exposure original plate before the exposure is conducted.
The pellicle is generally composed of a rectangular pellicle frame, a pellicle film attached in a slack-free manner to an upper end face of the pellicle frame, an airtight gasket formed on a lower end face of the pellicle frame, as well as other minor parts. The pellicle film exhibits a high transmittance with respect to an exposure light; and the said airtight gasket, generally made of an adhesive, is meant to glue the pellicle to the photomask, hence called an agglutinant.
If such a pellicle is installed on the photomask, the foreign matters do not directly adhere to the photomask for they are intercepted by and caught on the pellicle. Then, in the photolithography step, if the focal point is aligned with the pattern described on the photomask, the foreign matters on the pellicle are off the focal point and hence their images are not transferred, and thus the problems such as deformation of the pattern can be solved.
Now, in the photolithography technology, with the densification of patterns, shortening of the wavelength of the exposure light source has been progressed as a measure for increasing the resolution. To date, the exposure light source has shifted from g-line (436 nm) and i-line (365 nm) by mercury lamp to KrF excimer laser (248 nm) and ArF excimer laser (193 nm), and furthermore, the use of EUV (Extreme Ultra Violet) light with a dominant wavelength of 13.5 nm is also being studied.
On the other hand, with the furthering of the densification of the pattern, the agglutinant for gluing the pellicle to the photomask is being required to have scarce shortcomings and higher reliability, while up until now it could pass inspections if only it could glue the pellicle to the photomask even when it contained more or less air bubbles in it. However, if such bubbles are mixed in the agglutinant layer, which is laid and shaped on the lower end face of the pellicle frame, problems such as inadequate adhesion occur when the pellicle is glued to the photomask.
Therefore, IP Document 1 teaches to form a coating layer of a silicone resin over the pellicle frame surface as a measure to prevent the air captured in pits, cavities or holes in the surface of the pellicle frame from entering and forming small air bubbles in the agglutinant layer. However, this measure has a problem in that the manufacturing cost is increased due to the added process of creating such coating layer.
Furthermore, recently, with the increasing densification of the patterns, the deformation of the photomask which is caused when the pellicle is glued to the photomask has become one of the major problems. In order to suppress such type of deformation of the photomask, the agglutinant layer is being demanded to have higher uniformity in quality than before and is no longer permitted to contain fine air or gas bubbles, while at the same time it is required to maintain minimum necessary adhesive strength.